It is common to mount an LED die on a submount (a substrate) and position a pre-formed dome lens over the LED die to encapsulate it. The dome lens has a cavity for the LED die that contains a transparent or translucent resilient silicone. The bottom of the lens is otherwise flat. When the dome lens is pressed over the LED die, the silicone fills the voids around the LED die.
With such a structure, the light emission is generally lambertian. Light emitted from the sides of the LED die or at a shallow angle is frequently wasted light since the useful light emission is generally the light emitted in a forward direction. Such encapsulated LED dies have been mounted in small reflective conical cups to direct all the light in the forward direction, but such cups add cost and size to the LED module.
Additionally, light emitted in a downward direction may be absorbed somewhat by the submount surface and reflected at a shallow angle. Therefore, this light may also be wasted.
What is needed is a lens encapsulation technique that does not suffer from the drawbacks mentioned above.